The increasing importance of reducing radioactive waste quantities at nuclear facilities has made the concentration of all types of waste highly desirable. One such waste is boric acid slurries. More efficient evaporators are now capable of producing boric acid concentrations at nuclear power plants of greater than 50% by weight. The current method for solidifying high concentrations of borated waste is by solidification with hardeners such as cement. This method involves the addition of Portland cement and various other additives necessary to combat retardation of cement hydration by the boron. The packaging efficiencies (waste volume/product volume) achieved by cement solidification is limited to about 0.80, and several days are required to pass before the material can be transported. Ion exchange resins are sometimes found in the boric acid waste slurries and represent a further hindrance to cement solidification.
U.S. Pat. No. 4,122,028, issued on Oct. 24, 1978 to Iffland et al, describes a process for solidifying and eliminating radioactive borate containing liquids. Slaked lime and Portland cement are added to the boron containing aqueous solution and up to 30% of the cement can be replaced by silica or kieselguhr. Water glass and phosphoric acid or hydrogen phosphate can be added to increase strength, accelerate setting and improve resistance to leaching. The borate is usually present in the waste liquid of sodium borate, but may be present as potassium borate or boric acid.
U.S. Pat. No. 3,298,960, issued on Jan. 17, 1967 to Pitzer, describes a method for disposal of waste solutions using rigid gels. The gel products are formed by the addition of sodium silicate or formaldehyde to certain metal cleaning waste solutions. One such solution contains metal corrosion products dissolved in hydrazine and EDTA.
U.S. Pat. No. 3,507,801, issued on Apr. 21, 1970, describes a process for entrapment of radioactive waste water using sodium borate. After the sodium borate is added to the waste water the mixture is thickened by heating until the remaining quantity of water is no larger than can be bonded as water of crystallization to the sodium borate. This concentrate is drained into the containers where it cools and crystallizes, the water being incorporated into the solid crystals.
U.S. Pat. No. 3,988,258, issued on Oct. 26, 1976 to Curtis et al, describes a process for disposal of radioactive waste by incorporating it into a hardenable matrix-forming mass. Alkali or alkaline earth silicate is added to a cement-type binding agent to form the matrix material. The process is said to promote solidification of all common nuclear power industry radioactive waste including boric acid solutions.
As noted above, previous waste disposal processes using hardeners such as cement to produce a solidified product employed antihydration retardants to quicken the setting of the cement in the presence of the waste. One such antihydration retardant employed is sodium metasilicate, used not only with boric acid bearing wastes, but also with a variety of other wastes such as oils. When used with cement, sodium metasilicate functions to quicken setting of the cement in the presence of various waste products.